Delivery of diagnostic or therapeutic agents to the prostate is difficult. Current practice requires systemic administration, such as by intravenous, intramuscular, oral, transdermal, or intranasal routes, using doses which result in significant exposure to healthy tissues and relatively low exposure within the prostate gland. Frequently the systemic exposure leads to unwanted or harmful side effects which limit the usefulness of the therapeutic agent in treating prostate disease.
Targeted and local delivery strategies have been explored to minimize peripheral exposure with limited success. Some targeting strategies rely on prostate cells to express specific receptors to which a drug-targeting ligand complex binds. These receptors may not always be present, limiting the utility of the approach. The receptor density on prostate cells also can vary widely and restrict the actual amount of drug delivered to the prostate. In addition, other cells in the body may also express the same receptor leading to unwanted drug exposure. Lastly, the drug targeting ligand complex can be degraded prior to reaching the prostate, defeating the targeting mechanism.
Direct injection into or near the prostate also has been tried. Patient acceptance is low due to the pain and risk of infection. In addition, the mean residence time of the drug often is relatively short, which necessitates the use of multiple injections for treatment. Furthermore, the disruption of prostate tumors during injection can lead to metastasis. Depot formulations extend the drug presence in the prostate but reduce the amount of drug that can be injected into the prostate and may enhance local tissue toxicity.
Radionucleotide-containing pellets placed near the prostate are used to treat prostate cancer but provide only one treatment modality. Radiation therapy is also non-selective, leading to significant damage to surrounding healthy tissue structures including nerves.
The use of a suppository or drug eluting stent placed in the prostatic urethra is known, but these are difficult to place and poorly tolerated in men. Furthermore, these delivery means have a limited payload capacity.
Accordingly, there remains a need for improved drug delivery methods and systems for treating the prostate, such as in the treatment of prostate cancer or prostatitis.